Under the 3GPP standards, a NodeB (or an eNB in LTE) is a base station via which mobile devices connect to the core network. The 3GPP standards body has also adopted an official architecture and started work on a new standard for home base stations to provide short range 3G radiofrequency (RF) coverage. Where the home base station is operating to provide a UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network (UTRAN) type cell, the home base station is sometimes referred to as an HNB. Where the home base station is operating in accordance with the (Long Term Evolution) LTE standards to provide an LTE or evolved UTRAN (E-UTRAN) cell, the home base station is sometimes referred to as an HeNB. Where the home base station is operating to provide a UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network (UTRAN) type cell, the home base station is sometimes referred to simply as an HNB. A similar architecture will also be applied in the WiMAX network. In this case, the home base station is commonly referred to as a femto cell. For simplicity, the present application will use the term HeNB to refer to any LTE home base station, the term HNB to refer to UMTS/UTRAN home base stations, and the term home base station generically to refer to HNB, HeNBs or other such base stations. Each home base station will provide radio coverage (for example, 3G/4G/WiMAX) within the home, small and medium enterprise, shopping Malls etc and will sometimes connect to the core network via a suitable residential gateway and public or corporate broadband access network (for example via an ADSL link to the Internet).
The functionality of a home base station is often provided by a so called ‘femto access point’ (FAPs) and the term ‘home base station’ and ‘femto access point’ are often used interchangeably. An FAP can comprise a single mode FAP which provides the functionality of a single home base station operating a cell of a particular radio access technology (e.g. UTRAN or E-UTRAN). An FAP can also comprise a dual mode (or possibly multimode) FAP which provides the functionality of two (or possibly more) home base stations each effectively operating a cell of a different radio access technology (e.g. a UTRAN cell and an E-UTRAN cell).
In order to provide for mobility from one cell of the communications network to another, each FAP has a network monitor mode (NMM) functionality that allows it to scan for neighbouring cells and to place information, such as cell IDs or the like, relating to the neighbouring cells detected during the scan into a neighbour table or database at the FAP. In order to initiate the NMM and start scanning for neighbouring cells, the FAP must first stop downlink communication in the cell(s) that it operates. However, if there are any active mobile telephones connected via the FAP, the FAP cannot terminate downlink transmissions without disrupting the communication of the active mobile telephone(s). Accordingly, the FAP has to wait until the active mobile telephone(s) are no longer connected, before initiating the NMM, resulting in an associated, potentially undesirable, delay.
In the case of dual mode (or multimode) FAPs, which are more likely to be serving an active mobile telephone than a single mode FAP, a delay is more likely. Further, the possible number of active mobile telephones being served by a dual mode (or multimode) FAP when the NMM is to be initiated is likely to be higher than for a single mode FAP. This can lead to inefficiencies in the NMM scanning process. Moreover, scanning by the plurality of home base station components of a dual (or multimode) FAP can lead to a relatively high energy consumption because the scanning via each home base station component consumes energy meaning that the cumulative energy consumption is potentially higher than for scanning via a single mode FAP.
Accordingly, there is a need for a communication system in which one or more of the above issues is overcome or at least ameliorated.